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Abstract. Noise in Holocene paleoclimate reconstructions can hamper the detection of centennial to millennial climate variations and diagnoses of the dynamics involved. This paper uses multiple ensembles of reconstructions to separate signal and noise and determine what, if any, centennial to millennial variations influenced North America during the past 7000 years. To do so, ensembles of temperature and moisture reconstructions were compared across four different spatial scales: multi-continent, regional, sub-regional, and local. At each scale, two independent multi-record ensembles were compared to detect any centennial to millennial departures from the long Holocene trends, which correlate more than expected from random patterns. In all cases, the potential centennial to millennial variations had small magnitudes. However, at least two patterns of centennial to millennial variability appear evident. First, large-scale variations included a prominent Mid-Holocene anomaly from 5600–5000 yr BP that increased mean effective moisture and produced temperature anomalies of different signs in different regions. The changes shifted the north–south temperature gradient in mid-latitude North America with a pattern similar to that of the North Atlantic Oscillation (NAO). Second, correlated multi-century (∼ 350 years) variations produce a distinct spectral signature in temperature and hydroclimate records along the western Atlantic margin. Both patterns differ from random variations, but they express distinct spatiotemporal characteristics consistent with separate controlling dynamics.
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Multi-scale transects of three North American drylines
North American drylines are distinct air mass boundaries that have often been examined for their relation to the initiation of severe convective storms. Three cases of drylines occurring in synoptically quiescent environments are analyzed using data obtained from a single mobile platform in concert with data from operational synoptic and mesoscale observing systems. Very distinct moisture contrasts were noted in a nocturnal April case in mountainous terrain in the Trans-Pecos region of West Texas. The other two cases revealed multi-step moisture transitions within synoptically diffuse moisture gradients. Their evolution over time suggests that such multi-step patterns may be associated with diurnal and geographic forcing transitions, as well as positioning of deep moist convection.
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- Award ID(s):
- 1644888
- PAR ID:
- 10300264
- Date Published:
- Journal Name:
- Atmosphere
- Volume:
- 11
- Issue:
- 8
- ISSN:
- 2073-4433
- Page Range / eLocation ID:
- 854
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/doi:10.3390/atmos11080854
